Vaccines, including those containing live virus, inactivated virus, virus-like particles, viral protein subunits and combinations thereof, are thermolabile and to overcome the instability barrier, vaccine products are typically stored in a dried state. The labile nature of vaccines renders drying of vaccines a challenging task and often requires long conservative freeze-drying cycles (usually cycle times in excess 48-72 hrs) to obtain dried thermostable vaccines. Historical approaches to obtain dried vaccine and biologics hinges mostly on the use of lyophilizer and to a limited extent on spray-drying. However, vaccines, even if dried using these methods, have thus far failed to achieve adequate long-term room temperature stability.
Lyophilization (freeze-drying) processes typically entail freezing the vaccine components and then drying by sublimation. Removal of the solvent and substitution by a matrix comprising protective molecules such as sugar molecules, may increase the stability of the protein by preventing degradation and denaturation of this protein. U.S. Pat. No. 5,565,318 describes the use of a polymeric sugar as a protective agent in the formation of room temperature stable semi-spheres containing biologicaly active materials. U.S. Patent Application Publication No. 20100297231 describes foam-forming formulations comprising a biologically active protein and a polyol. U.S. Patent Application Publication No. 20110243988 describes the use of polyols as a stabilizer for dry powder live virus vaccines. International Patent Application Serial No. PCT/EP2013/064422 describes the preservation of biologically active protein by freeze-drying in a protective matrix comprising a sugar.
Microwave vacuum-drying is a rapid method that can yield products, such as foods, plants and biological materials, with improved stability compared to air-dried and freeze-dried products. Because the drying is done under reduced pressure, the boiling point of water and the oxygen content of the atmosphere is lowered, so food or medicinal components sensitive to oxidation and thermal degradation can be retained to a higher degree than by air-drying. See, e.g., U.S. Pat. Nos. 4,389,794; 4,664,924; 4,809,596; 4,882,851; 6,128,321; 6,956,865; and International Patent Application Publication Nos. WO 02/103407; WO 2009/033285; WO 2009/049409; and WO2013/010257.
Seo et al., 2004, Journal of Non-Crystalline Solids, 333:111-114 discloses a method for making sugar glass without caramelization of the sugar through the use of microwaves.
There is a desire for increased heat stability, especially in the developing world where transport, storage, and administration costs (mainly due to the need of continuous refrigeration, also referred to as the “cold chain”) represent a significant portion of the product cost.